This invention relates to the art of ink jet printing and more particularly to an improved ink jet tip assembly for ink jet printers and a method for manufacturing same.
Ink jet printers are known in the art as shown, for example, in U.S. Pat. Nos. 3,298,030 and 3,683,212. Ink jet printers are used in a wide variety of printing operations such as computer printout, business systems printers, or notation devices for intermittently operated recording charts. They are particularly useful in printing operations where high speed is required, where large numbers of or unusual characters are required, or where silent printing is desired. However, the manufacture of tip assemblies for these printers has heretofore been a time consuming and cumbersome operation with the tip assemblies thus produced having a relatively high instance of failure.
In these prior art ink jet printers, the tip assemblies have required a relatively high voltage to effect sufficient oscillation of a piezoelectric transducer element. In order to produce sufficient mechanical energy to achieve ejection of ink droplets over a long period of time in commercial applications, voltages on the order of 85 to 110 volts were required.
Relatively low oscillation frequencies of the prior art tip assemblies have undesirably retarded the printing speed for ink jet printers. The prior art tip assemblies normally were only capable of oscillation at frequencies on the order of a few kilohertz. Although the piezoelectric elements were capable of being oscillated at higher frequencies, the bonding together of the nozzle and piezoelectric element were not sufficiently consistent to facilitate efficient transfer of higher frequency vibrations from the piezoelectric element to the nozzle.
The glass ink nozzle in prior tip assemblies was normally anchored to the piezoelectric element with an electrically conductive, silver filled epoxy resin. This epoxy resin typically filled a small gap between the piezoelectric element and the glass nozzle. However, the gap was so small that the air required for the epoxy to cure was denied easy access. This caused the curing to take place slowly and irregularly over a long period of time. Also, as the epoxy cured, its characteristics, especially its vibratory energy transfer characteristics, changed and thereby caused the overall operating characteristics of the tip assemblies to change.
The irregular curing of epoxy further caused the required operating voltage and oscillating frequency to change with time. Those few tip assemblies which would operate at a low voltage or a high frequency one time could not be relied upon to operate at the same low voltage or high frequency during subsequent operations. There was a general tendency for epoxy bonded tip assemblies to require higher operating voltages and lower operating frequencies as they aged.
Further, epoxy adheres strongly to glass. In assembling the glass nozzle and the piezoelectric element, the nozzle outlet orifice tended to become plugged and because this orifice is very small, it was not readily cleanable. To alleviate these problems, special assembly techniques such as dipping, the tip of the nozzle into wax were employed. This resulted in a two-step nozzle orifice clearing process of first removing the epoxy from the wax and then removing the wax from the orifice.
Recently epoxy has been identified as a possible carcinogen. Thus, the prior assembly techniques noted above present safety hazards to workers closely involved therewith.
The present invention contemplates new and improved tip assembly arrangements and a method for making same which overcomes all of the above-referred problems and others and provides a tip assembly which is simple and inexpensive to manufacture and which has improved operating characteristics. These characteristics include faster printing speeds and greater ink dispensing capabilities as well as a more reliable overall tip assembly construction.